Currently Microsoft Teams integration with Flow is available in terms of "actions" (https://ms.flow.microsoft.com/en-us/services/shared_teams/microsoft-teams/). It would be useful to be able to have "triggers" from Microsoft Teams to enable scenarios such as "when a new message is posted in a channel" take "some" action...
The Teams connector now supports triggers. You can read about these new triggers here: https://flow.microsoft.com/blog/support-tickets-teams-sharepoint/